Hi

im a 20yo and i've recently discovered a lump on the back of my neck. I first noticed it about two months ago but it's gotten slightly bigger around the size of a marble now. You can't see it but I can feel it under my skin. It doesn't hurt to touch 

Im also extremely tired all the time as well as chest discomfort but ive had this for a couple of years so not sure it's related.

I tend to also feel sick quite a lot.

Furthermore, i've also had a sense of pressure in my stomach and then pain that comes and goes on the right side and more flatulence than normal (sorry if it's tmi)

Not sure if this is all related but any advice would be extremely appreciated thank you